The Microbiology Core Unit is to established to fulfill the following specific objectives: 1. Ongoing support for the P3 (Children's Respiratory Study-CRS) project. This includes continued detection (cultures and/or serologies) of viruses, mycoplasma, ureaplasma, and chlamydia, in order to define, as completely as possible, the causative agents of acute lower respiratory illnesses (LRI) in infants and children. In addition, P3 studies will be extended to include specific investigations of other infectious agents which: 1) may be significantly involved in LRI; 2) may be associated with long term sequelae; and 3) have not yet been systemically sought. These include: a) Human respiratory coronaviruses (OC43 and 229E), including development and applicationof monoclonal antibody methods to detect viral antigens and conduct seroepidemiologic investigations. b) Epstein-Barr virus antigens and conducts seroepidemiologically to define its relative contribution to LRI and long-term sequelae among the P3 subjects, either as a possible primary etiologic agent, or as an associated factor contributing to enhanced susceptibility to other infections. c) Other agents which have not been previously detected by standard methods to date will be investigated seroepidemiologically by the use of indirect immunofluorescent and/or hemagglutination-inhibition methods. These include influenza type C and parainfluenza type 4 viruses. 2. Virologic and serologic support for the P5 and P6 projects.